Extensible Application Markup Language
|Internet media type||
|Initial release||v1.0 / June 2008|
|Latest release||v2009 / 16 April 2010|
|Type of format||User interface markup language|
Extensible Application Markup Language (XAML, i//) is a declarative XML-based language created by Microsoft that is used for initializing structured values and objects. It is available under Microsoft's Open Specification Promise. The acronym originally stood for Extensible Avalon Markup Language - Avalon being the code-name for Windows Presentation Foundation (WPF).
XAML is used extensively in .NET Framework 3.0 & .NET Framework 4.0 technologies, particularly Windows Presentation Foundation (WPF), Silverlight, Windows Workflow Foundation (WF) and Windows Runtime XAML Framework. In WPF, XAML forms a user interface markup language to define UI elements, data binding, eventing, and other features. In WF, workflows can be defined using XAML. XAML can also be used in Silverlight applications, Windows Phone apps and Windows Store apps.
XAML elements map directly to Common Language Runtime object instances, while XAML attributes map to Common Language Runtime properties and events on those objects. XAML files can be created and edited with visual design tools like Microsoft Expression Blend, Microsoft Visual Studio, and the hostable Windows Workflow Foundation visual designer. They can also be created and edited with a standard text editor, a code editor like XAMLPad, or a graphical editor like Vector Architect.
Anything that is created or implemented in XAML can be expressed using a more traditional .NET language, such as C# or Visual Basic.NET. However, a key aspect of the technology is the reduced complexity needed for tools to process XAML, because it is based on XML. Consequently, a variety of products are emerging, particularly in the WPF space, which create XAML-based applications. As XAML is simply based on XML, developers and designers are able to share and edit content freely amongst themselves without requiring compilation. Since it is strongly linked to the .NET Framework 3.0 technologies, the only fully compliant implementation at present is Microsoft's.
A XAML file can be compiled into a .BAML file (Binary Application Markup Language), which may be inserted as a resource into a .NET Framework assembly. At run-time, the framework engine extracts the .BAML file from assembly resources, parses it, and creates a corresponding WPF visual tree or workflow.
When used in Windows Presentation Foundation, XAML is used to describe visual user interfaces. WPF allows for the definition of both 2D and 3D objects, rotations, animations, and a variety of other effects and features.
When used in Windows Workflow Foundation contexts, XAML is used to describe potentially long-running declarative logic, such as those created by process modeling tools and rules systems. The serialization format for workflows was previously called XOML, to differentiate it from UI markup use of XAML, but now they are no longer distinguished. However, the file extension for files containing the workflow markup is still "XOML".
This Windows Presentation Foundation example shows the text "Hello World!" in the top-level XAML container called Canvas.
<Canvas xmlns="http://schemas.microsoft.com/client/2007" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"> <TextBlock>Hello World!</TextBlock> </Canvas>
The schema (the xmlns="http://schemas.microsoft.com..." part) may have to be changed to work on your computer. Using a schema that Microsoft recommends, the example can also be
<Canvas xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"> <TextBlock>Hello World!</TextBlock> </Canvas>
The MySilverlight.js file must contain the code that loads the above XAML code (as an XML file) under the MySilverlight html element.
Differences between versions of XAML 
There are four Microsoft main implementations of XAML:
- The Windows Presentation Foundation version, which is used for the .NET Framework beginning with .NET Framework 3.0
- The Silverlight 3 version
- The Silverlight 4 version
- The Windows 8 XAML/Jupiter version
These versions have some differences in the parsing behavior.
Additionally, the XAML parsing between Silverlight 3 and Silverlight 4 is not 100% forwards compatible; XAML files which are accepted by Silverlight 3 may not be accepted or parsed differently in Silverlight 4.
The European Committee for Interoperable Systems has said that Microsoft's use of XAML in its Silverlight product aims to introduce content on the World Wide Web that can only be accessed from the Windows platform. Using a plugin, XAML is viewable in some non-Microsoft browsers on Windows and Mac, and Microsoft provides direct support for Novell's development of a Silverlight viewer for GNU/Linux called Moonlight. As of January 2010, Moonlight 2 is a compatible implementation of Silverlight 2, but development of Moonlight has since been discontinued.
See also 
- Comparison of user interface markup languages
- Layout manager
- List of user interface markup languages
- NextStep/Cocoa Interface Builder
- Open XML Paper Specification
- Microsoft (2006-06), [MS-XAML] – v1.0, Xaml Object Mapping Specification 2006, Copyright © 2008 Microsoft Corporation. Release: June 2008 (PDF), retrieved 2010-06-24
- Microsoft (2010-04), [MS-XAML] – v2009, XAML Object Mapping Specification 2009, Copyright © 2010 Microsoft Corporation. Release: April 2010 (PDF), retrieved 2010-06-24
- Microsoft (2010-04-16), Extensible Application Markup Language (XAML), retrieved 2010-06-24
- Microsoft adds XAML to 'Open Specification' list - Software Development Times On The Web
- Rob Relyea : January 2004 - Posts
- "XAML Syntax Terminology". Microsoft Corporation.
- unknown (2009-07-30). "What is BAML?". http://www.dotnetspider.com/: DOTNET Spider. Retrieved 2011-08-18. "BAML means Binary Application Markup Language, which is a compiled version of the XAML. When you compile your XAML it creates the BAML file."
- MSDN forum post by the WF product manager
- RuleML and BPEL are other examples of XML-based declarative logic languages
- Guthrie, Scott (2008-02-22). "Silverlight Tutorial Part 7: Using Control Templates to Customize a Control's Look and Feel". Retrieved 2008-03-08.
- Microsoft XAML Overview page at XAML Overview (Root element and xmlns)
- Windows Presentation Foundation on the Web: Web Browser Applications - MSDN
- "XAML Processing Differences Between Silverlight Versions and WPF". Microsoft. Retrieved 2011-10-02. "Silverlight includes a XAML parser that is part of the Silverlight core install. Silverlight uses different XAML parsers depending on whether your application targets Silverlight 3 or Silverlight 4. The two parsers exist side-by-side in Silverlight 4 for compatibility. In some cases, the XAML parsing behavior in Silverlight differs from the parsing behavior in Windows Presentation Foundation (WPF). WPF has its own XAML parser."
- "http://msdn.microsoft.com/en-us/library/ff457753%28v=vs.95%29.aspx". Microsoft. Retrieved 2011-10-02.
- "Microsoft runs into EU Vista charges". itwire.com. 2007-01-28. Retrieved 2008-04-16.
- Foley, Mary Jo (2007-09-25). "Microsoft officially ‘extends support’ for Novell’s Silverlight Linux port". zdnet.com. Retrieved 2007-10-13.
- "Releasing Moonlight 2, Roadmap to Moonlight 3 and 4". Miguel de Icaza. Retrieved 2009-12-17.